Use bnd 2.3 (via maven-bundle-plugin 2.5.3) to avoid java 8 import problems

java 8 adds the source class of constant references to the constant pool, causing unaware bnd's to generate bogus import-package clauses. c.f. http://blog.bjhargrave.com/2014/04/java-8-bnd-and-references-to-compile.html

Apparently this is fixed in bnd 2.3 which is used in maven-bundle-plugin 2.5.3.